BLDC control!

Discussion in 'General Electronics Chat' started by engstudent08, Oct 21, 2008.

  1. engstudent08

    Thread Starter New Member

    Oct 21, 2008
    Hey guys lets see if anyone can help me here :

    I have a MOOG BLDC motor and after several weeks of research I'm starting my design :
    Vm=330, Max RPM 6000, IC = 6A ..
    Now the main problem I have is that the MOOG motor is very old! it has a resolver mounted on it. I'm am trying to figure out how i can determine the rotor position ? Most techniques for commutation control involve using embedded hall effect sensors..

    Are there any experiments people know off on how i can determine this rotor position ? given that there is no room on the shaft after i attach the gear to mount a position encoder.

    does anyone know how i can use the resolver, i have the data sheet and location of the s1 s2 ect... but i am worried. What if the resolver was not aligned at zero.. it is an old motor.. what if the MOOG control system accounted for this missalignment?

    I am building a electric go-kart, capable of reaching approx 60km, all my prelim cals say this motor can do it, its just a matter of controlling it. I want max torque so i want to allign the rotor flux and stator current at 90degs.

    But how i use the resolver data.. if i can.. baffels me.
    given that i dont need micron accuracy as in a CNC machince for example are there any other techniques I could use to control the commutation of this motor ??

  2. scubasteve_911

    Senior Member

    Dec 27, 2007
    Do you know what your resolver actually outputs? Is it the three hall-effect signals? If so, then you must ensure it is mounted as it was. If it provides an incremental type signal (with A and B quadrature signals), then commutation must be inferred. Typically, this is done with open-loop commutation at a speed that is slower than your J (dw(t)/dt). When the rotor is locked on, you will start reading predictable incremental pulses, then set your commutation points (if using 6-step, for example) in your microcontroller.

    So, this motor is very old? Why not try to get a company to donate it for the project? How are you getting 330V @ 6A? To step up battery voltages to that level, you'll need more than a simple boost regulator. You will have to use a flyback of some sort.

    You know this isn't very safe! What if you crash and a HV connection touches you? If you're going to spend money and time into a go-kart, get a motor that is replaceable. What if you designed everything around some old motor, then it fails?

  3. scubasteve_911

    Senior Member

    Dec 27, 2007
    Secondly, you know that you will be getting about 2.3HP from this. Is this enough?

    You should probably also know that you can only get the 2.3HP when the motor is going the full speed and under rated load. This means, you will need to gear the go-kart accordingly to get constant power across your range.